Oil sorbent devices are very well known in the art. They come in shapes of sheets, sweeps, blankets, pads, pillows, mats, etc., in many different sizes. Rather thin (normally no thicker than ½ inch) nonwoven polypropylene or cotton sheets, sweeps, blankets, pads are commonly used for collection of oil on solid surfaces and water, and widely described in the suppliers brochures and literature (e.g. The Basics of Oil Spill Cleanup by Mery Fingas, The Second Edition, pp. 105-106).
Another type of absorbent are fibrous granulated sorbents which may be loose (particulate, granular, fibrous) and are used for absorbing oil, after an oil spill, and other hydrocarbons on water and dry surfaces. All known the sorbents can be classified into three major groups including natural inorganic sorbents, natural organic sorbents, and synthetic sorbents. A fourth group of sorbents may be engineered sorbents.
Natural inorganic (mineral) sorbents include clay, sand, perlite, vermiculite, etc. These sorbents have relatively high density, and after they are spread on the surface of a body of water they sink. It has been found that treatment of these mineral sorbents with hydrophobic agents does not provide them with sufficient and prolonged buoyancy on the surface of water. In addition, another drawback of mineral sorbents is their relatively low oil sorption, or oil sorbency ratio (weight of absorbed oil divided by original “dry” weight of the sorbent), which is usually below 2.
Natural organic sorbents include various vegetable fibre, cellulose, wood sawdust and chips, corncob components, rice hulls, peanut shells, straw, peat moss, etc. While these organic sorbents are biodegradable a major drawback to them is that they sink, which is a problem with most of natural organic sorbents, which is harmful to the environment.
There are several patents relating to hydrophobic non-sinking fibrous sorbents. For example, U.S. Pat. No. 3,770,575 discloses oil sorbent materials prepared from cellulose pulp which have been treated with a sizing material to render the fibers water repellant. U.S. Pat. No. 4,670,156 discloses a hydrophobic sorbent, which is prepared by subjecting a water-containing, fibrous cellulosic product, particularly sulphite reject fibers, to rapid heating to cause expansion of the fibers through gasification of the water therein. U.S. Pat. No. 5,021,390, Hatton teaches a composition for absorbing liquids consisting of various fibrous plant materials (wood fibers, bagasse, grass, rice hulls and corn husks) treated with the waterproofing agent sodium methyl silicate. U.S. Pat. No. 5,492,881 teaches a sorbent system using finely ground cellulose treated with a hydrophobic agent such as paraffin, other waxes, polyvinyl alcohol, hydroxyl-ethyl cellulose, or the like.
A general shortcoming of all the above mentioned natural organic sorbents is the relatively low sorption ratios, which is typically about 2 to 3 and practically does not go above 5 to 6. Another disadvantage of the natural cellulose sorbents is that, even when treated by water repellent agents, they have only a partial and temporary hydrophobicity, so that in time they break down and absorb water. When picking up water, they sink below the level of the oil and the water takes up much of their sorption capacity. So there is little room remaining for absorption of oil.
U.S. Pat. No. 6,027,652 discloses a naturally hydrophobic sorbent fiber material produced from agricultural byproducts including cultivation of banana, plantain, cavendish plant, pineapple, coconut, palm, or other tropical fruit bearing plants. However the availability of such fibers is not sufficient for large scale production of sorbents, especially in the regions where these fruits are not cultivated.
The above described natural organic and inorganic sorbents come in the form of powders or fibers, which creates another problem, namely difficulty in their spreadability on oil spills and their collection with the absorbed oil, as well as dusting. This problem is addressed in part by U.S. Pat. No. 6,092,302 which proposes absorbent fibrous granules. The granulated absorbent has essential advantages from point of its distribution and collection in compare to absorbent in form of powder or fibers. One problem with the granules according to the U.S. Pat. No. 6,092,302 is that they are “a cellulosic-based”, i.e. made from naturally hydrophilic fibers, and accordingly have limitation for use in aqueous environments. Another drawback is the high cost of the granules, since they are made by “wet” method with subsequent power-intensive and expensive drying process. Further, cellulosic-based granules have a relatively low oil sorption typical for cellulose sorbents in general.
The synthetic loose sorbents are reputed to have high oil sorption capacity and may be made from polyurethane, polyethylene, polypropylene and polyester, and come in the form of chunks, cubes, powders, fibers, etc. French Patent No. 2,460,987 discloses a powdered oil sorbent made from a semi-rigid or rigid polyurethane foam. These polymer materials in their known forms have the same problems as those mention above with respect to the inorganic and organic sorbents, namely difficulty in spreading them onto oil spills, dusting, and problematic collection with absorbed oil. With respect to collection of the oil filled sorbents, the synthetic sorbents are not biodegradable per se, and therefore it is desirable to completely recover them from water or land after their use.